Catalyst cartridge for carbon dioxide reduction unit

ABSTRACT

The catalyst cartridge has an inner cylindrical perforated wall and an outer cylindrical perforated wall concentric with the inner wall and spaced radially therefrom. One end of the cartridge is closed by a circular base. The other end of the cylindrical cartridge is closed by a circular covering having a central aperture therein for admitting a mixture of hydrogen and carbon dioxide gas through a supply pipe having an electric heater therein. The outer surface of the inner wall and the inner surface of the outer wall, and the inner surfaces of the base and cover caps are covered with a batting of quartz wool which encloses within the space defined a catalyst material or iron in the form of uniformly packed steel wool.

United States Patent [191 Fletcher et al.

[ Nov.-l3, 1973 CATALYST CARTRIDGE FOR CARBON DIOXIDE REDUCTION UNIT[76] Inventors: James C. Fletcher, Administrator of the NationalAeronautics and Space Administration with respect to an invention of;Roy F. Holmes, 4240 Morrell St., San Diego, Calif. 92109 221 Filed: Oct.21, 1971 21 Appl. No.: 191,301

[52] U.S. Cl. 23/288 J, 23/288 F, 23/252 R, 23/281, 423/231, 128/19] R,55/510, 55/518 [51] Int. Cl B0lj 9/04, BOld 53/34 [58] Field of Search23/288 F, 288 J, 23/252 R, 281; 423/217, 218, 220, 230, 231;

[56] References Cited UNITED STATES PATENTS 3,421,826 1/1969 Tope eta1. 1. 23/288 F X 3/1970 Bois 23/288 F UX 2/1970 Zeff et al 23/280 F X[57] ABSTRACT The catalyst cartridge has an inner cylindrical perforatedwall and an outer cylindrical perforated wall concentric with the innerwall and spaced radially therefrom. One end of the cartridge is closedby a circular base. The other end of the cylindrical cartridge is closedby a circular covering having a central aperture therein for admitting amixture of hydrogen and carbon dioxide gas through a supply pipe havingan electric heater therein. The outer surface of the inner wall and theinner surface of the outer wall, and the inner surfaces of the base andcover caps are covered witha batting of quartz wool which encloseswithin the space defined a catalyst material or iron in the form ofuniformly packed steel wool.

6 Claims, 4 Drawing Figures P TENIEn m1 3 191a 3771. 959

\k CONDENSER K HEAT 7/ 22 EXCHANGER SEPARATOR J J I 1 M2 R x26 2 3LIQUID 2 t -|0 2? FIG. 1

COMPRESSOR z 6 FIG 4 INVENTOR.

ROY F. HOLMES ATTORNEYS CATALYST CARTRIDGE FOR CARBON'DIOXIDE REDUCTIONUNIT ORIGIN OF THE INVENTION The invention described herein was made inthe performance of work under a NASA contract and is subject to theprovisions of Section 305 ofthe National Aeronautics and Space Act of1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).

BACKGROUND OF THE INVENTION Field of the Invention This inventionrelates generally to life support systems of the type utilized in spacevehicles. One of the functions of the life support system in brief is toremove the carbon dioxide produced by crew members from the spaceship orspacesuit atmosphere, and to reclaim oxygen from the carbon dioxide. Oneknown method for accomplishing this utilizes the Bosch process whichcatalytically reacts hydrogen with carbon dioxide to produce water andsolid carbon. The water is then electrolyzed to yield hydrogen for reusein the Bosch reaction and oxygen for the crew. In previously employedsystems utilizing the Bosch reaction, there have been a number ofdifficulties encountered.

The primary problem which has prevented the full realization of theBosch reaction in life support systems has been the prevention of anyreaction in parts of the system where carbon deposits cannot betolerated. In continuous removal reactors, migration of the carbonresulting from the reaction has not been successfully controlled and inbatch removal systems, its migration from reaction zone or formationoutside the reaction zone has not been prevented.

It is an object of this invention to provide a replaceable catalystcartridge for a life support system utilizing the Bosch reaction for thereduction of carbon dioxide whereby total carbon containment is achievedwithin the desired reaction zone. It is also an object of this inventionto guarantee that the carbon dioxide reduction takes place in thereaction'zone only and that the product carbon formed in the reactionzone is retained within the reaction 'zone and does not migrateelsewhere in the system'carrying catalyst with it, thus preventing anycarbon formation reaction taking place outside the reaction zone.

The Bosch catalytic reaction .is carried out at temperatures generallyin the range of l,000 to 1,400F and may be represented by the followingoverall chemical equation:

The intermediate reactions which take place indlude the following: 1 r CC0, C 2 2C0 and 2H C 2 CH which combined yield the following overallrepresentation: xH +yC Z aH O bC 'cCO dCl-I,

wherein x 2y, and a, b, c, and d are variable with time,

temperature, pressure, and initial concentrations of the reactants.

SUMMARY OF THE INVENTION This invention comprises a catalyst cartridgeparticularly for utilization in a carbon dioxide reducing apparatus in alife support system for space vehicles. The catalyst cartridge includesan inner perforated metal wall, an outer perforated wall spacedoutwardly from the inner wall, a base plate closing one end of thecartridge, and a cover plate closing the other end of the cartridge. Thecover plate has a central aperture therein through which a supply linehaving a heater therein feeds a gaseous reaction mixture comprisinghydrogen and carbon dioxide at a temperature from about 1,000F to about1,400F. The outer surfaces of the internal wall and the inner surfacesof the outer wall are lined with a ceramic fiber batting material ofsufficient thickness to prevent carbon formed in the reaction frompassing through it. The portion of the surfaces of the base and coverplates defined within the inner and outer walls are likewise lined withceramic batting, thus forming a complete enclosure lined with suchbatting. Contained within the enclosure of the batting is an ironcatalyst for the reaction. The heated reaction mixture passes outwardlythrough the inner perforated wall and ceramic batting and over thecatalyst. The solid carbon product formed is retained within theenclosure containing the catalyst. The water vapor and unreacted carbondioxide and any intermediate products pass through the perforations ofthe outer wall. No reaction takes place outside the area containing thecatalyst and any migration of the catalyst bearing carbon is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings:

FIG. 1 is a schematic of a system utilizing the catalytic cartridge ofthis invention for the reduction of carbon dioxideby means of the Boschreaction.

FIG. 2 is. an end view of the catalyst cartridge of this invention. 7

FIG. 3 is a side sectional view of the catalyst cartridge of thisinvention, taken along line 33 of FIG. 2.

FIG. 4 is a perspective view of the assembled catalyst cartridge of thisinvention mounted on the end of the reactor case of the system of FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A system for reducing carbondioxide to carbon and water utilizing the Bosch reaction is shown insche' matic form in FIG." lot the accompanying drawings. There is showna reactor 2 within which the catalyst cartridge 4of this invention ismounted on the base 3 of the reactor 2. A mixture of hydrogen and carbondioxide is fed'to the system through feed line 6 which leads to acompressor 8. The compressor pumps the gases through feed line 10 toheat exchanger 12 wherein the mixture is heated to approximatelyreaction temperature and then from the heat exchanger 12 passesthroughsupply line. 14 to the reactor 2. The line 1-4 has an electricheater 16 in the end 15 which passes through the cover 40 into thecenter of the catalyst cartridge 4, as shown in FIG. 3. As representedby the heavy arrows 68, a mixture of reacted and unreacted gases passesfrom the catalyst cartridge 4 into the outer portion 5 of the reactor 2,and thereafter out through drogen and oxygen. The oxygen is thenresupplied to I the crew members and the hydrogen returned forutilization in the carbon dioxide reduction process. The other gasesfrom the reaction are recycled through line 28 and mixed together withthe hydrogen and carbon dioxide gas in line 6. A reactor thermocouplewell 7 extends to the outside of the reactor 2 from the cartridge 4.

The catalytic cartridge 4 of this invention is shown in greater detailin FIGS. 2, 3, and 4. The mixture of hydrogen and carbon dioxide gasenters the interior of the cartridge 4 from the supply line 14 at theend 15. The gas entering has been heated to a reaction temperature ofapproximately 1,000 to 1,400F by the electric heater shown schematicallyat 16 near the end of the line 14.

The cartridge 4 includes an outer cylindrical metal wall 30 havingperforations 32 therein, and an inner cylindrical metal wall 34 havingperforations 36 therein. The inner and outer cylindrical walls areretained between a base plate 38 and a cover 40. The base plate 38 has acircular flange 39 extending over one'end of outer metal wall 30 and thecover 40 has a similar flange 41 extending over the other end of thewall 30. The cover 40 has a central aperture 42 through which the supplyline 14 passes. A smaller aperture 44 in the cover 40 is provided for acartridge thermcouple well 46 which extends into the space definedbetween the inner and outer cylindrical walls and the base and coverplates.

Apertures 49 and 51 in the flanges 39 and 41 of the base plate 38 andcover 40 respectively are provided for retaining one end of clips 50.The other end of the clips 50 is inserted into a perforation 32 in theouter wall 30 thus securing the base 38 and cover plate 40 to the outerwall 30.

As shown most clearly in FIG. 3, the inner surfaces of the outerperforated wall 30, the outer surface of the inner perforated wall 34,and the inside surface of the base 38 and cover 40, are covered with alayer of ceramic wool bat as shown at 52, 54, 56, and 58, respectively.The preferred embodiment is quartz wool battingQOther suitable knownceramic fiber battingssuch as high temperature glass may be utilizedprovided they are non-catalytic in the reaction, and chemicallyunaffected by prolonged exposure to the reaction environment. Theselection of such materials is within the competence of those skilled inthe art.

As indicated, the catalyst for the Bosch process is iron. The catalystis preferably used in a fiber-like form such as steel wool. If toocoarse a form of iron is used, there is less surface area and theprocess accordingly does not run efficiently.

The use of the steel wool as the source of the catalytic iron isdesirable since it will readily support the Bosch reaction and remainsuniformly distributed within the reaction zone of the catalystcartridge, as well-as providing support to retain the initial carbondeposited prior to build-up of a carbon block structure.

Since during the reaction process, iron diffuses into the resultingcarbon product without losing its catalytic activity, this diffusioncauses fairly rapid deterioration of a fine steel wool fiber. Shoulddisintegration of the steel wool fiber occur before a sufficient amountof carbon has formed to support the iron and to maintain a fairlyuniform distribution throughout the reaction zone, flow channels woulddevelop and adversely effect the rate of the process. A coarser grade ofsteel wool disintegrates more slowly and thus allowing time for thegrowth of the supporting carbon block.

In the embodiment shown, no. 2 steel wool is packed firmly into theenclosure defined by the inner and outer walls and the base and cover.

As indicated by the heavy arrows 68 in FIG. 3, the mixture of carbondioxide, hydrogen gas and any recycled gases flows from the interior ofthe cartridge inner wall 34 through the perforations 36 thereof, andthrough the catalyst 60. As the reaction takes place, carbon deposits 66begin to build up in the mesh of the steel wool catalyst 60. The watervapor resulting from the reduction of carbon dioxide in the reaction,together with unreacted hydrogen, carbon dioxide, carbon monoxide andmethane, emerges from the cartridge 4 as shown by the arrows at 68 afterpassing through the catalyst 60, the outer ceramic batting 52, and theperforations 32 in the outer wall 30.

Most importantly, there is no migration of catalystbearing carbonoutside of the reaction zone. The reaction takes place entirely withinthe confines of the reaction zone defined by the quartz wool batting inthe cartridge and the migration of carbon and catalyst to other parts ofthe system is prevented, thus eliminating reaction in other parts of thesystem and subsequent clogging of the system by carbon deposits.

The metal surfaces of the catalytic cartridge, reactor, and heatexchanger must be non-catalytic under the reaction conditions of theBosch reaction, that is, the high temperatures and reducing atmosphere.Selection of such materials is within the purview of those skilled inthe art.

In the above embodiment, the base 38 and the cover 40 of the cartridgeare spun from type 321 stainless steel. The inner and outer walls 34 and30 are rolled and welded from type 304 stainless steel, perforated with3/32 inch holes on 5/32 inch centers. Allapertures are punched prior toplating. The parts are then plated with an electrolytic nickel strikefollowed by 1 to 2 mils of electroless nickel. The thermocouple well 46is alloy 122 phosphorous-dioxidized copper and the cover clips 50 areInconel X-750. The reactor body and other parts which are exposed tohighjtemperature gases are type 321 stainless steel with electrolyticnickel strike, 1 mil of electroless nickel, 4 mils of nickelelectroplate. The thermocouple well 46 is inserted in the aperture 44 inthe cover 40 and locked to the cover 40 with a pressfit copper retainingwasher 45. The cover 40 is fastened to the outer wall 30 with the clips50. The quartz wool liner for the base and inner and outer walls is theninserted. All liners are held temporarily in place by a sheet metalshield while the steel wool catalyst is added. The steel wool should bepacked uniformly with special attention given to the region around thethermocouple well 46 in order to eliminate any voids which would lead tochanneling of the reaction gases. The shield is then removed and thebase 38 with its liner 56 put in place and fastened with the clips 50.The assembledcartridge 4 is then secured to the end 3 of the reactor 2by means of the brackets 70. Then the cartridge 4 is positioned insidethe reactor 2-with thesupply line 14 projecting through the aperture 42of the cover 40 into the area enclosed by the inner wall 34. Thethermocouple well 7 attached to the reactor 2 projects into thecartridge thermocouple well.46.

The cartridge in the above embodiment is about 7% inches in diameter andeleven and three-quarters inches in length. The dimensions of theresulting carbon block after allowing for the quartz wool liners are anoutside diameter of 7 inches and an inside diameter of 2% inches with alength of about 1 1% inches. The cartridge weighed about 2.85 poundswhen packed with 150 grams of no. 2 steel wool. Approximately 0.17 poundof quartz wool batting was employed.

A cartridge of this invention of the size utilized in the aboveembodiment is capable of reducing the carbon dioxide given off by fourmen for a period of at least three days. With such a cartridge thissystem can be operated with pressure drops between the inlet of the feedgases into the cartridge and the'outlet of the reacted gases of up topsi. The carbon formed in the cartridge as a result of the reduction ofthe carbon dioxide can build up to a density of about 0.5 grams per cc.before it is necessary to replace the cartridge in order to maintain anefficient reaction rate.

Inspection of a system utilizing the cartridge of this invention after400 hours of operation shows the system to be free of any carbondeposits outside of the reaction zone.

While the Bosch reaction can be carried out at temperatures of from1,000 to 1,400F., it has been found that preferably the reaction shouldbe maintained at l,l50 to 1,300F, with the most preferred range being1,240 to l,270F. and the ideal temperature 1,250F. This is convenientlymaintained by adjustment of the current flow in the electric heater 16.

The cartridge described in the foregoing embodiment can treat up to 10pounds of carbon dioxide per day removing at least 3,450 grams ofcarbon. in a typical day of operation the unit removed 9.28 pounds ofcarbon dioxide, consumed 0.85 pounds of hydrogen to yield 7.6 pounds ofwater and 2.53 pounds of carbon. The flow rate of gases was 144 poundsper day. The composition of the recycled gases typically comprised on avolume .bass about 40 percent hydrogen, 30 percent methane, percentcarbon monoxide, and 10 percent carbon dioxide.

in practice, it has been found that in order to decrease the time toinitially establish the Bosch reaction, the iron catalyst should bepre-activated by etching. Typically, the steel wool catalyst is treatedwith a 3 percent hydrochloric acid solution for 2 to 5 minutes, and thenrinsed with distilled water and finally dried in an oven at 230F forabout minutes, prior to packing the cartridge. With this treatment theprocess usually stabilizes at a normal rate in about 1.5 hours. If thecatalyst is not pre-activated, it usually takes about 3 to 8 hours tostabilize the process on initial start up and it may take up to 10 to 12hours.

- While the invention has been explained by a detailed description of aspecifc embodiment, it is understood that various modifications andsubstitutions can be made within the scope of the appended claims whichare intended to include'equival'ents of such embodiment.

What is claimed is:

1. A replaceable cylindrical catalyst cartridge for use in a lifesupport system utilizing the Bosch reaction for the reduction of carbondioxide comprising:

a housing,

said housing including an inner tubular perforated wall, an outertubular perforated wall spaced outwardly from said inner perforatedwall, and a base closing one end of said housing,

a cover closingthe other end of said housing, said cover being providedwith a centrally located aperture having a smaller cross-section thanthat of said inner perforated wall for admitting a carbon dioxidereaction mixture,

a layer of ceramic fiber covering the outer surface of said inner wall,the inner surface of said outer wall, and the inner surfaces of saidbase and said cover defined between the ends of said inner and outerwalls, and i a catalyst contained within the space defined by the innerand outer walls, and said base and said cover,

said catalyst having the inherent physical property characteristic ofcatalyzing the reduction of carbon dioxide to carbon and water in thepresence of hydrogen and in the temperature range of 1 ,000l,400F.

2. A catalyst cartridge as claimed in claim 1 wherein said catalyst isan iron catalyst in the form of activated steel wool.

3. A replaceable catalyst cartridge comprising an inner cylindricalperforated wall, an outer cylindrical perforated wall spaced radiallyfrom said inner perforated wall, a circular base closing one end of saidcartridge, a circular cover closing the other end of said cartridge,said cover having a centrally located aperture therein through which agaseous reaction mixture comprising carbon dioxide and hydrogen may beadmitted, said inner wall, outer wall, base, and cover each beingcomprised of metal and having the inherent physical propertycharacteristic of being non-reactive in a reducing atmosphere attemperatures up to 1,400F, a

' layer of ceramic fiber covering the outer surface of said inner wall,the inner surface of said outer wall, and the inner surfaces of saidbase and said cover defined between the ends of said inner and outerwalls, and an iron catalyst contained within the space defined by saidinner and outer walls and said base and said cover.

4. A cartridge as claimed in claim 3 wherein'said iron catalyst is inthe form of steel wool.

5. A cartridge as claimed in claim 4 wherein said ceramic fiber is inthe form of quartz wool batting.

6. A cartridge as claimed in claim 5 wherein said steel wool has beenactivated, by etching with dilute hydrochloricjacid. I

2. A catalyst cartridge as claimed in claim 1 wherein said catalyst isan iron catalyst in the form of activated steel wool.
 3. A replaceablecatalyst cartridge comprising an inner cylindrical perforated wall, anouter cylindrical perforated wall spaced radially from said innerperforated wall, a circular base closing one end of said cartridge, acircular cover closing the other end of said carTridge, said coverhaving a centrally located aperture therein through which a gaseousreaction mixture comprising carbon dioxide and hydrogen may be admitted,said inner wall, outer wall, base, and cover each being comprised ofmetal and having the inherent physical property characteristic of beingnon-reactive in a reducing atmosphere at temperatures up to 1,400*F, alayer of ceramic fiber covering the outer surface of said inner wall,the inner surface of said outer wall, and the inner surfaces of saidbase and said cover defined between the ends of said inner and outerwalls, and an iron catalyst contained within the space defined by saidinner and outer walls and said base and said cover.
 4. A cartridge asclaimed in claim 3 wherein said iron catalyst is in the form of steelwool.
 5. A cartridge as claimed in claim 4 wherein said ceramic fiber isin the form of quartz wool batting.
 6. A cartridge as claimed in claim 5wherein said steel wool has been activated by etching with dilutehydrochloric acid.